Derivation of aerosol properties from satellite measurements of backscattered ultraviolet radiation: Theoretical basis

Abstract

Abstract. We discuss the theoretical basis of a recently developed technique to characterize aerosols from space. We show that the interaction between aerosols and the strong molecular scattering in the near ultraviolet produces spectral variations of the backscattered radiances that can be used to separate aerosol absorption from scattering effects. This capability allows identification of several aerosol types, ranging from nonabsorbing sulfates to highly UV-absorbing mineral dust, over both land and water surfaces. Two ways of using the information contained in the near-UV radiances are discussed. In the first method, a residual quantity, which measures the departure of the observed spectral contrast from .that of a molecular atmosphere, is computed. Since clouds yield nearly zero residues, this method is a useful way of separately mapping the spatial distribution of UV-absorbing and nonabsorbing particles. To convert the residue to optical depth, the aerosol type must be known. The second method is an inversion procedure that The consequent aerosol effect on climate is usually quantified in terms of radiative forcing, i.e., the net flux change at the top of the atmosphere due solely to the direct aerosol radiative effects. Although there are uncertainties in the estimates of aerosol radiative forcing, it is generally agreed that the averaged global direct effects of anthropogenic sulfate aerosols are In spite of the difficulties inherent with satellite-based sensing, spaceborne measurements remain the most convenient method to characterize aerosol particles and determine their time and space distribution on a global basis. Currently available satellite data sets on aerosol properties do not provide a full description of the atmospheric aerosol load. The advanced very high resolution radiometer (AVHRR) aerosol data set provides information on optical depth only over the water surfaces of the Earth. The SAM and SAGE family of sensors were specifically designed to retrieve information on strato-17,099

Retrieval of Asian Dust Amount over Land using ADEOS-II/GLI near UV Data

“…In previous aerosol retrieval studies with UV spectral region such as the Direct Method, the aerosol layer height used to be assumed as some constant values. However, a difference in aerosol layer height assignment by 1 km, possibly causes up to 70 % retrieval error in optical thickness (Torres et al 1998). Fortunately, we had a simultaneous LIDAR observation at the Shapotou site.…”

“…Based upon the above residual method, Torres et al (1998) developed the Direct Method, so-called "the method retrieves optical thickness and single scattering albedo of UV-absorbing aerosols such as dust and soot". The method was applied to the TOMS long-term dataset (around 20 years) for semi-global analyses of aerosol optical thickness (Torres et al 2002).…”

Absorbing Aerosols and Summer Monsoon Evolution over South Asia: An Observational Portrayal

“…The TOMS project has produced the longest available global record of aerosol observations in terms of AI, and a number of studies have demonstrated its feasibility and success (e.g., Torres et al 1998;Chiappello et al 1999;Hsu et al 1999;Cakmur et al 2001;Prospero et al 2002;Duncan et al 2003). Monthly data on a 1.25°ϫ 1°grid are available on the TOMS Web site (http://toms.gsfc.nasa.gov/aerosols/aerosols_v8.html).…”

Long-range transport of mineral dust in the global atmosphere: Impact of African dust on the environment of the southeastern United States

“…Recently, the Total Ozone Mapping Spectrometer (TOMS) instrument has been used for detecting absorbing aerosols based on the spectral contrast at 340 and 380 nm in the upwelling ultraviolet spectrum (13). TOMS is sensitive to UV-absorbing aerosols such as mineral dust, volcanic ash, and soot aerosol from fossil fuel combustion sources and biomass burning.…”

“…Also, the AI is not a quantitative measure of aerosol concentration. TOMS is sensitive to a number of aerosol physical properties and, of most importance, to the altitude of the aerosols layer (13). Fig.…”